1. Field of the Invention
The present invention relates to a recording medium conveyance method and apparatus applied to image forming apparatuses such as copying machines, printers, facsimiles and inkjet printers, and a storage medium that contains a control program for use in controlling the recording medium conveyance apparatus.
2. Description of Related Art
FIG. 8 is a schematic diagram showing the internal structure of a conventional image forming apparatus (e.g., a copying machine, a printer, a facsimile and an inkjet printer). In FIG. 8, reference numeral 801 denotes a photosensitive drum, which forms a toner image from a latent image. Reference numeral 802 denotes a laser scanner, which depicts a latent image on the photosensitive drum 801, and 803 a tone developer, which puts toner on the latent image on the photosensitive drum 801. Reference numeral 804 denotes a feeding roller 804, which feeds a recording medium (e.g., recording paper) P, described later. Reference numeral 805 denotes a transfer part, which transfers an image onto the recording medium P and separates the recording medium P from the photosensitive drum 801 (recording medium separating part), and 806 a toner fixing part, which fixes the toner on the recording medium P. Reference numeral 807 denotes a post-separation sensor, which senses a separation jam, 808 a reader part, which reads an image, and 809 a pair of resist rollers, which stops and feeds the recording medium P according to a control sequence before the recording medium P is fed to the transfer part 805. Reference numeral 810 denotes a transfer electrifier, which transfers a toner image on the photosensitive drum 801, 811 a separation electrifier, which separates the recording medium P from the photosensitive drum 801, and 812 a cleaning means, which removes the toner residing on the photosensitive drum 801. Symbol P designates recording paper as the recording medium.
FIG. 9 is a schematic diagram showing the internal structure of parts around a photosensitive drum of a conventional image forming apparatus. In FIG. 9, reference numeral 901 denotes a photosensitive drum as an image carrier, which forms a toner image from a latent image, and 902 a part, which transfers an image on a recording medium (e.g., recording paper) 906, described later, and then separates the recording medium 906 from the photosensitive drum 901. Reference numeral 903 denotes a cleaning means that removes toner residing on the photosensitive drum 901, and 904 a separation electrifier, which separates the recording medium 906 from the photosensitive drum 901. Reference numeral 905 denotes a post-separation sensor, which senses a separation jam, and 906 the recording medium. FIG. 9 shows a state wherein the recording medium 906, which is poorly separated from the photosensitive drum 901, is passing the lower side of the photosensitive drum 901.
FIG. 10 is a schematic diagram showing an input from the outside of a conventional image forming apparatus. In FIG. 10, reference numeral 1001 denotes a conveyance belt, which conveys a recording medium by electrostatic absorption, and 1001a and 1001b belt driving rollers for driving the conveyance belt 1001. Reference numeral 1002 denotes an absorption electrifier for absorbing the recording medium onto the conveyance belt 1001, 1003 a separation electrifier, which separates the recording medium from the conveyance belt 1001, and 1004 a post-separation sensor for detecting a separation jam. Reference numeral 1005 denotes a pair of resist rollers, which stops and feeds the recording medium before the recording medium is fed to a transfer part, and 1006 a photosensitive drum as an image carrier, which forms a toner image describing a latent image.
FIG. 11 is a diagram showing a conventional method of detecting a separation delay jam. In FIG. 11, reference numeral 1101 denotes a resist clutch signal that is an actuating signal from a resist clutch, which operates the pair of resist rollers (denoted by 809 in FIG. 8 and 1005 in FIG. 10). Reference numeral 1102 denotes a sensor signal from the post-separation sensor (denoted by 807 in FIG. 8, 905 in FIG. 10 and 1004 in FIG. 10). Reference numeral 1103 denotes a point in time where the resist clutch is operated. Reference numeral 1104 denotes a jam detection timing. Reference numeral 1105 indicates that a sensor signal 1102 is High, and 1106 indicates that a sensor signal 1102 is Low.
There will now be given some examples of separation devices provided in an image forming apparatus such as a copying machine, a printer, a facsimile and an inkjet printer, which separate a recording medium such as paper, an OHP, a board and a cloth. If the image forming apparatus is a copying machine and the recording medium is paper, a first example of the separation devices is a device that transfers images depicted on the photosensitive drum 801 as the image carrier onto sheets of paper, which are conveyed on a sheet-by-sheet basis from the feeding part 804 in FIG. 8, and then electrostatically separates the paper from the photosensitive drum 801.
A second example of the separation devices is a device that is provided in a copying machine having the conveyance belt 1001 in FIG. 10 and applies an electric current to the absorption electrifier 1002, absorbs the paper onto the conveyance belt 1001, transfers an image depicted the photosensitive drum 1006 as the image carrier onto the paper by the transfer electrifier 1007, separates the paper from the photosensitive drum 1006 and then separates the paper from the conveyance belt 1001 by the separation electrifier 1003.
If the image forming apparatus is an inkjet printer, an example of the separation devices is a device that separates the recording medium from a head member, which forms an image by jetting ink.
Referring next to FIG. 8, a brief description will be given of the entire operation of the image forming apparatus having the separation device as the above-mentioned first example.
In FIG. 8, a laser beam emitted from the laser scanner 802 is irradiated onto the photosensitive drum 801, which is rotating clockwise as viewed in the figure. This forms an electrostatic latent image on the photosensitive drum 801, and the tone developer 803 visualizes the electrostatic latent image. The laser scanner 802 emits a laser beam according to an original image read by the reader part 808. On the other hand, sheets of the recording medium P, which are stacked in a recording medium cassette, not shown, are fed from the cassette. The feeding roller 804, which is rotating counterclockwise as viewed in the figure, sequentially feeds the sheets of the recording medium P stacked in the recording medium cassette from the top one on a sheet-by-sheet basis. The recording medium P fed from the recording medium cassette is sent to the pair of resist rollers 809, which are not rotating. Each sheet of the recording medium P stops moving when it abuts against a nip of the pair of resist rollers 809 and forms a predetermined amount of loop. This corrects oblique movement of the recording medium P, so that an image can be recorded on the recording medium which is in a correct position. The recording medium P, after having been corrected from the oblique position, is conveyed to the transfer part 805 between the photosensitive drum 801 and the transfer electrifier 810 by the pair of resist rollers 809 which start rotation in predetermined timing. While the recording medium P is passing the transfer part 805, the transfer electrifier 810 transfers a toner image onto the photosensitive drum 801. During the transfer of the toner image, the recording medium P is electrostatically absorbed onto the photosensitive drum 801, but is separated from the photosensitive drum 801 by the separation electrifier 811. The recording medium P, which has been properly separated from the photosensitive drum 801, is guided to reach the post-separation sensor 807 in proper timing. The conveyed recording medium P is then sent to the toner fixing part 806, which heats and pressurizes the recording medium P to fix the toner image which has been unfixed. Upon completion of the fixing process, the recording medium P is discharged onto a discharge tray, not shown, outside the image forming apparatus.
A detailed description will now be given of the operation of the recording medium separating part. After the image depicted the photosensitive drum 801 is transferred onto the recording medium P by the image transfer part 805, an electric current is applied to the separation electrifier 811 to separate the recording medium P from the photosensitive drum 801. If this separation is not well done, the recording medium P moves in a state held in contact with the photosensitive drum 801, and this may result in damage to the cleaning means 812, etc. on the photosensitive drum 801.
Any of the separation devices mentioned above has the possiblity of damage to a part or parts inside of the apparatus body if the recording medium moves in in a state held in contact with a non-contact body (e.g., the photosensitive drum 801).
To eliminate this disadvantage, conventionally, a recording medium conveyance part after the recording medium separating part has a recording medium detecting means 807, and whether the sensor output signal indicating a state of the recording medium from the post-separation sensor (807 in FIG. 8, 905 in FIG. 9 and 1004 in FIG. 10) is High (1105 in FIG. 11) or Low (1106 in FIG. 11) is determined upon the passage of a predetermined period of time which was set at a designing stage (in the image forming apparatus in FIG. 8 for example, 500 ms after the generation of an actuating signal from the resist clutch for actuating the pair of resist rollers 809 (the pair of resist rollers 1005 in FIG. 10), which temporarily stop the recording medium P fed sheet by sheet from the feeding roller 804, start rotating after the generation of an image formation signal and feed the recording medium P to the transfer part) (1101, 1103 and 1104 in FIG. 11). If the output signal from the post-separation sensor is High, the recording medium P is determined as jamming and then the recording medium conveying part is stopped (1105 in FIG. 11).
A current value applied to a separation electrifier member (the separation electrifier 811 in FIG. 8 and the separation electrifier 904 in FIG. 9) for use in separating the recording medium from the image carrier is constant in an atmosphere (i.e., moisture and temperature) in which the image forming apparatus is placed, although conventionally there was an image forming apparatus which determines the atmosphere and change the current value according to the atmosphere.
Although conventionally there was a device for cleaning the separation electrifier, which is used to separate the recording medium from the image carrier, a cleaning member of that device is regularly operated, e.g., whenever a predetermined number of sheets of the recording medium have passed the device or when a predetermined period of time has passed after a power supply is turned on.
In the prior art, however, as described above, the detection of a jam at the recording medium separating part is carried out by determining whether the output signal from the post-separation sensor (807 in FIG. 8, 905 in FIG. 9 and 1004 in FIG. 10) is High (1105 in FIG. 11) or Low (1106 in FIG. 11) after the lapse of a predetermined period of time set at the designing stage (e.g., 500 ms after the generation of the resist clutch actuating signal) (1101, 1103 and 1104 in FIG. 11). For example, High indicates the presence of the recording medium, and the recording medium is determined as jamming if the output signal from the post-separation sensor is High. If the output signal is Low, the recording medium is not determined as jamming.
Since the jam detection timing is constant in the above case, the recording medium passing after the jam detection timing is indiscriminately determined as jamming even if there is no problem in respect of the separation performance. This causes temporal and economic damage to a user since he or she is required to spend much time dealing with the jam and pay extra copying fees.
An explanation will now be given of timing in which the recording medium passes through the post-separation sensor (807 in FIG. 8, 905 in FIG. 9 and 1004 in FIG. 10). If the number of passing sheets of the recording medium is increased, it becomes impossible to apply a proper separation current to the recording medium due to dirt, etc. of the separation electrifier member. For example, the recording medium 906 passes through the separation part as shown in FIG. 9 in a fashion being wound around the image carrier (the photosensitive drum 901). Therefore, as shown in a graph of FIG. 12 wherein the abscissa represents passage timing and the ordinate represents the number of passing sheets of recording medium, there is such a tendency that minimum passage timing Tmin becomes smaller, maximum passage timing Tmax becomes larger, hence mean passage timing Tmean is delayed, and a standard deviation "sgr" of the passage timing becomes larger, as will be learned from a comparison between a line 1201 and a line 1202. Thus, if the jam timing Tjam is fixed, a further increase in the number of sheets of recording medium may make it impossible for the recording medium to pass through the post-separation sensor before the jam timing Tjam. In this case, even a properly separated sheet of recording medium is determined as jamming.
Further, since the current value applied to the separation electrifier is almost constant in the atmosphere in which the apparatus is placed, the current value may be unsuitable for separating the recording medium from the image carrier or the conveyance belt depending upon the state of the image carrier (the photosensitive drum 801 in FIG. 8) or the conveyance belt (1001 in FIG. 10). In this case, the recording medium cannot be separated satisfactorily, and this results in phenomena such as a poor image and jamming.
It is therefore a first object of the present invention to provide a recording medium conveyance method and apparatus, which can prevent a properly conveyed recording medium from being determined as jamming to thereby avoid an unnecessary operation of dealing with a jam and can further prevent degradation in the separation performance of an electric separation means for the recording medium.
It is a second object of the present invention to provide a storage medium that contains a control program for controlling the above-mentioned recording medium conveyance apparatus of the present invention.
To attain the first object, in a first aspect of the present invention, there is provided a recording medium conveyance method for conveying a recording medium, comprising a recording medium separation step of separating a moving recording medium in contact with a member on the recording medium, from the member, a recording medium detecting step of detecting the recording medium at a predetermined location downstream of the recording medium separation step, a timing measuring step of measuring timing in which the recording medium passes the predetermined location downstream of the recording medium separation step in accordance with passage timing information acquired in the recording medium detecting step, a passage timing storing step of storing the passage timing information acquired in the timing measuring step, a statistic calculation step of executing a statistic calculation to acquire statistically calculated passage timing information in accordance with the passage timing information stored in the passage timing storing step, and a control step of executing a control in such a manner as to perform a predetermined operation in accordance with the statistically calculated passage timing information acquired in the statistic calculation step.
Typically, the recording medium is paper.
Preferably, the statistic calculation step comprises calculating a mean value of the measured timing.
Also preferably, the statistic calculation step comprises calculating a standard deviation of the measured timing.
Preferably, the statistic calculation step comprises calculating maximum passage timing of the recording medium.
Also preferably, the statistic calculation step comprises calculating minimum passage timing of the recording medium.
Further preferably, the statistic calculation step comprises calculating percentage of frequency of passage of the recording medium through the predetermined location in timing other than predetermined timing.
More preferably, the statistic calculation step comprises calculating at least two of a mean value of the measured timing, a standard deviation of the measured timing, maximum passage timing of the recording medium, and minimum passage timing of the recording medium.
Preferably, the control step comprises controlling timing of detecting a jam of the recording medium.
Also preferably, the control step comprises giving a warning of a change in the statistically calculated passage timing information.
The recording medium conveyance method according to the first aspect may further comprise a separation electrifying member cleaning step of cleaning a separation electrifying member for use in the recording medium separation step, and a second control step of controlling the separation electrifying member cleaning step in accordance with the statistically calculated passage timing information acquired in the statistic calculation step.
To attain the first object, in a second aspect of the present invention, there is provided a recording medium conveyance apparatus for conveying a recording medium, comprising recording medium separation means for separating a moving recording medium in contact with a member on the recording medium, from the member, recording medium detecting means for detecting the recording medium at a predetermined location downstream of the recording medium separation means, timing measuring means for measuring timing in which the recording medium passes the predetermined location downstream of the recording medium separation means in accordance with passage timing information acquired by the recording medium detecting means, passage timing storing means for storing the passage timing information acquired by the timing measuring means, statistic calculation means for executing a statistic calculation to acquire statistically calculated passage timing information in accordance with the passage timing information stored by the passage timing storing means, and control means for executing a control in such a manner as to perform a predetermined operation in accordance with the statistically calculated passage timing information acquired by the statistic calculation means.
To attain the first object, in a third aspect of the present invention, there is provided an image forming apparatus comprising transfer means for transferring a toner image carried on an image carrier, onto a recording medium, separation means for separating the recording medium from the image carrier, detection means for detecting the recording medium separated by the separation means, and control means for controlling the separation means in accordance with a detected result of the detecting means.
Preferably, in the image forming apparatus according to the third aspect, the control means controls an electric current applied to the separation means.
Also preferably, the image forming apparatus according to the third aspect further comprises storage means for storing timing in which the recording medium is detected by the detection means.
To attain the first object, in a fourth aspect of the present invention, there is provided an image forming apparatus comprising transfer means for transferring a toner image carried on an image carrier, onto a recording medium, separation means for separating the recording medium from the image carrier, detection means for detecting the recording medium separated by the separation means, determination means for determining a jam in accordance with a result of the detection by the detection means, and control means for controlling a threshold value for determination of the jam by the determination means in accordance with the result of the detection by the detection means.
Preferably, the image forming apparatus according to the fourth aspect further comprises storage means for storing timing in which the recording medium is detected by the detection means.
To attain the first object, in a fifth aspect of the present invention, there is provided an image forming apparatus comprising transfer means for transferring a toner image carried on an image carrier, onto a recording medium, separation means for separating the recording medium from the image carrier, detection means for detecting the recording medium separated by the separation means, and cleaning means for cleaning the separation means in accordance with a result of the detection by the detection means.
Preferably, the image forming apparatus according to teh fifth aspect further comprises storage means for storing timing in which the recording medium is detected by the detection means.
To attain the second object, in a sixth aspect of the present invention, there is provided a storage medium storing a computer readable program for controlling a recording medium conveyance apparatus for conveying a recording medium, the program comprising a program code for causing a computer to execute a recording medium conveyance method comprising a recording medium separation step of separating a moving recording medium in contact with a member on the recording medium, from the member, a recording medium detecting step of detecting the recording medium at a predetermined location downstream of the recording medium separation step, a timing measuring step of measuring timing in which the recording medium passes the predetermined location downstream of the recording medium separation step in accordance with passage timing information acquired in the recording medium detecting step, a passage timing storing step of storing the passage timing information acquired in the timing measuring step, a statistic calculation step of executing a statistic calculation to acquire statistically calculated passage timing information in accordance with the passage timing information stored in the passage timing storing step, and a control step of executing a control in such a manner as to perform a predetermined operation in accordance with the statistically calculated passage timing information acquired in the statistic calculation step.
The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.